Image data encoding and decoding and storage medium

Abstract

An image encoding apparatus comprises a selector configured to select, from a set of candidate prediction operations each defining at least a prediction direction selected from a set of available prediction directions, a prediction operation for prediction of samples of a current region of a current image, the current region comprising an array of two or more rows and two or more columns of samples; and an intra-image predictor configured to derive predicted samples of the current region with respect to one or more of a group of reference samples of the same image in dependence upon a prediction direction, defined by the selected prediction operation, between a current sample to be predicted and the reference samples; in which for at least some of the candidate prediction operations: the group of reference samples comprises two or more parallel linear arrays of reference samples disposed at different respective separations from the current region, the intra-image predictor being configured to derive the predicted samples in dependence upon reference samples of the two or more linear arrays pointed to by the prediction direction; each of the linear arrays comprises reference samples at image positions, relative to the current region, within a horizontal and vertical image position range of the current region dependent upon a size and/or shape of the current region; the apparatus comprises a sample generator configured to generate zero or more additional reference samples for at least one of the linear arrays at one or more additional reference sample positions outside the horizontal and vertical image position range of the current region, so that, taking into account the additional reference samples, the prediction direction points to a reference position within each of the linear arrays.

1 . An image decoding apparatus comprising:
 circuitry configured to perform intra prediction decoding by:   deriving reference samples from two or more parallel linear arrays of reference samples disposed at different respective separations from an image region for image regions to be decoded;   testing whether a reference sample in the two or more parallel linear arrays of reference samples is available for an intra prediction operation having a prediction direction, and, if a reference sample is unavailable, generating one or more substitute reference samples for unavailable reference samples;   filtering at least one of the one or more substitute reference samples generated; and   using the at least one substitute filtered reference sample in decoding an image.   
     
     
         2 . The apparatus according to  claim 1 , the one or more substitute reference samples are generated in dependence on the value or values of one or more available reference samples. 
     
     
         3 . The apparatus according to  claim 1 , wherein for an intra prediction operation using both of at least an available and at least a substitute reference sample, the circuitry is further configured to filter both of the available and the substitute reference samples. 
     
     
         4 . The apparatus according to  claim 1 , wherein the generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample. 
     
     
         5 . The apparatus according to  claim 1 , wherein the generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample prior to filtering the substitute reference sample. 
     
     
         6 . The apparatus according to  claim 5 , wherein an adjacent available sample is a substitute reference sample. 
     
     
         7 . The apparatus according to  claim 1 , wherein generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample when an unavailable reference sample is required in a set of reference samples required by an intra prediction operation. 
     
     
         8 . The apparatus according to  claim 1 , wherein an unavailable reference sample is in one of the one or more parallel linear arrays which is spatially separated from another of the parallel linear arrays. 
     
     
         9 . The apparatus according to  claim 8 , wherein the generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample, the adjacent available reference sample being in a parallel linear array which is spatially separated from another of the parallel linear arrays. 
     
     
         10 . The apparatus according to  claim 1 , wherein a substitute reference sample is not generated from data representing a second parallel linear array when the second parallel linear array is not available, the second parallel linear array being spatially separated from the image region to be decoded. 
     
     
         11 . The apparatus according to  claim 1 , wherein the substitute reference sample is used in a weighted calculation to derive a reference sample value with at least one other reference sample. 
     
     
         12 . The apparatus according to  claim 1 , wherein the apparatus is included in one of a video storage, capture, transmission or reception apparatus. 
     
     
         13 . An image decoding method comprising:
 performing intra prediction decoding by:   deriving reference samples from two or more parallel linear arrays of reference samples disposed at different respective separations from an image region for image regions to be decoded;   testing whether a reference sample in the two or more parallel linear arrays of reference samples is available for an intra prediction operation having a prediction direction, and, if a reference sample is unavailable, generating one or more substitute reference samples for unavailable reference samples;   filtering, by circuitry, at least one of the one or more substitute reference samples generated; and   using the at least one substitute filtered reference sample in decoding an image.   
     
     
         14 . The method according to  claim 13 , wherein the generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample. 
     
     
         15 . The method according to  claim 13 , wherein the generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample prior to filtering the substitute reference sample. 
     
     
         16 . The method according to  claim 13 , wherein generating the substitute reference sample comprises setting a value of the substitute reference sample equal to the value of an adjacent available reference sample when an unavailable reference sample is required in a set of reference samples required by an intra prediction operation 
     
     
         17 . The method according to  claim 13 , wherein an unavailable reference sample is in one of the one or more parallel linear arrays which is spatially separated from another of the parallel linear arrays. 
     
     
         18 . The method according to  claim 13 , wherein the substitute reference sample is used in a weighted calculation to derive a reference sample value with at least one other reference sample. 
     
     
         19 . The method according to  claim 1 , wherein the testing is performed only for samples pointed to by the prediction direction. 
     
     
         20 . A non transitory storage medium comprising computer code components which, when executed on a computer cause the computer to perform the method of  claim 13 .